In social science commodities frequently stand for economic rationality and commercial gain, while gifts are presumed to be bearers of moral obligation and social concerns. "Commodity versus gift" often acts as metaphor for "market versus non-market." From the perspective of Marxist political economy, the binary opposition between commodities and gifts is unwarranted. Analysis of the neglected role of use value in commodity exchange as well as of the relationship between substance and form of commodity value shows that commodities are not pure representatives of market relations. Rather, commodities rest on, and give rise to, non-market relations. Capitalist markets are sites of rational economic give-and-take, but also provide new terrain for trust, commitment, custom, and power among exchange participants. Non-market relations do not shrink inexorably in the capitalist mode of production, but are mobilized to sustain accumulation, especially through the credit system.